Apparatus for die-to-die communication

ABSTRACT

In described examples, a first die includes a primary LC tank oscillator having a natural frequency of oscillation to induce a forced oscillation in a secondary LC tank oscillator of a separate second die via a magnetic coupling between the primary LC tank oscillator and the secondary LC tank oscillator.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/244,929 filed Aug. 23, 2016, which is a continuation of U.S. patentapplication Ser. No. 14/289,895 filed May 29, 2014, which claimspriority to India Patent Application No. 2345/CHE/2013 filed May 29,2013, all of which are hereby fully incorporated herein by reference forall purposes.

TECHNICAL FIELD

This relates generally to electronic circuits, and more particularly toa method and apparatus for die-to-die communication.

BACKGROUND

In formation of an integrated circuit, a number of active and passivesemiconductor devices are fabricated within dies on a wafer. In amulti-chip module (MCM), multiple dies are mounted on a shared substrateor board. The MCM includes various numbers and combinations ofsemiconductor devices, such as processing devices, memory devices andwireless communication devices. In one example, between thesemiconductor devices on a first die and semiconductor devices on asecond die, the electrical isolation is potentially 1000s of volts. Fordie-to-die communication, example solutions include opto-couplers,radiative RF couplers, capacitive couplers and transformer couplers.However, those solutions have shortcomings. The performance ofopto-couplers is degraded because of a large variation in their currenttransfer ratios and because of aging related issues. Radiative RFcouplers use very high frequency (e.g., greater than 60 GHz) fordie-to-die communication. Also, they are relatively expensive to build,and their efficiency is low at low data rates due to system overhead.Capacitive couplers and transformer couplers have metal platesassociated with each die, which have various shortcomings, such as: (a)imposing a requirement of close proximity between those metal plates;(b) an amount of electrical isolation being dependent on a materialbetween the metal plates; (c) maximum voltage tolerance being limited byspacing between the metal plates; and/or (d) higher cost from a specialdie or a printed circuit board (PCB) for implementation of thedie-to-die communication.

SUMMARY

In described examples, a first die includes a primary LC tank oscillatorhaving a natural frequency of oscillation to induce a forced oscillationin a secondary LC tank oscillator of a separate second die via amagnetic coupling between the primary LC tank oscillator and thesecondary LC tank oscillator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a structural perspective view of apparatus, according to anembodiment.

FIG. 2 is a schematic diagram of an LC tank oscillator.

FIG. 3 is a schematic diagram of coupled LC tanks in operation of theapparatus of FIG. 1.

FIGS. 4A-4C are graphs of modulation operations performed in theapparatus of FIG. 1.

FIG. 5 is a structural perspective view of a first alternative versionof the apparatus of FIG. 1.

FIG. 6 is a structural perspective view of a second alternative versionof the apparatus of FIG. 1.

FIG. 7 is a structural perspective view of a third alternative versionof the apparatus of FIG. 1.

DETAILED DESCRIPTION

FIG. 1 is a structural perspective view of apparatus 100, according toan embodiment. The apparatus 100 includes at least a first die 105 and asecond die 110. The first die 105 and the second die 110 areillustrative, and the apparatus 100 may include multiple die and otheractive/passive components. The first die 105 includes at least a firstcircuit 115, and the second die 110 includes at least a second circuit120.

In a first embodiment, the first die 105 is integral with a firstconductive pad 125, and the second die 110 is integral with a secondconductive pad 130. The first conductive pad 125 and the secondconductive pad 130 both include multiple grooves to substantiallyprevent eddy current formation on the first conductive pad 125 and thesecond conductive pad 130 respectively. In a second embodiment, thefirst die 105 is integral with a first substrate (or chip) 125, and thesecond die 110 is integral with a second substrate (or chip) 130. In athird embodiment, the first conductive pad 125 and the second conductivepad 130 both include multiple cuts to substantially prevent eddy currentformation on the first conductive pad 125 and the second conductive pad130 respectively. In a fourth embodiment, when each of the first die 105and the second die 110 are integral with a non-conductive pad, thenon-conductive pad may optionally omit the multiple grooves.

In one example, the first die 105 and the second die 110 are integralwith a laminate, which substantially prevents eddy current formation. Ina further example, the first die 105 and the second die 110 are part ofdifferent packages, which are part of a PCB. In another example, theapparatus 100 is integral with an MCM, so that the first die 105 and thesecond die 110 are on a single chip in the MCM. In a different example,the apparatus 100 is integral with an MCM, so that the first die 105 andthe second die 110 are part of different chips in the MCM. In yetanother example, the apparatus 100 is integral with a PCB.

In one version, the first die 105 is symmetrical with the second die110, so that dimensions (e.g., length, width and height) of the firstdie 105 are same as dimensions of the second die 110. The first die 105is coplanar to the second die 110, so that the first die 105 and thesecond die 110 are in same plane. The first die 105 and the second die110 are positioned such that: (a) first surfaces of the first die 105and the second die 110 are on a chip (125 or 130); and (b) secondsurfaces (opposite from the first surfaces) of the first die 105 and thesecond die 110 are active surfaces containing the first circuit 115 andthe second circuit 120 respectively. In an embodiment, the first circuit115 is coplanar to the second circuit 120. The first die 105 and thesecond die 110 are separated by a fixed distance (d) 140. In oneexample, the fixed distance (d) 140 is more than 0.5 mm. In a furtherexample, the fixed distance (d) 140 varies from 0.5 mm to 1 mm(millimeters). In another example, the fixed distance (d) 140 is suchthat a high voltage isolation (e.g., above 1.5 kilovolt) is maintainedbetween the first die 105 and the second die 110.

The first circuit 115 and the second circuit 120 include respectiveantenna coils with non-radiative dimensions (e.g., non-radiative when anelectrical length of the antenna coil is less than one-eighth of anoperating wavelength of the apparatus 100). In one example, the firstcircuit 115 is on-chip, and its antenna coil is integral with alaminate. In another example, the antenna coil is a flat coil (e.g.,flat spiral coil) having N number of loops in one plane, where N is aninteger. In one version, the second die 110 is on top of the first die105, so that an active surface of the first die 105 is facing an activesurface of the second die 110, and each of those active surfacescontains its respective antenna coil. In one embodiment, the first die105 and the second die 110 are integral with a first package and asecond package respectively. In a further example, the second package ison top of the first package, such that the active surface of the firstdie 105 is facing the active surface of the second die 110.

In an embodiment, the loops of the antenna coil and a capacitor togetheroperate as an LC tank (inductor capacitor tank) oscillator. In oneexample, each of the first circuit 115 and the second circuit 120includes a respective LC tank oscillator that is formed by a set ofinductors and a set of capacitors. Also, each of the first circuit 115and the second circuit 120 includes a respective transmitter and arespective receiver, which are used for communication between the firstdie 105 and the second die 110.

The first circuit 115 is coupled to an energy source (not shown in FIG.1), such as a voltage source or a current source. In a first example,the first die 105 includes the energy source. In a second example, theenergy source is external to the first die 105. In a third example, theenergy source is external to the apparatus 100.

During operation of the apparatus 100, in response to a signal (e.g.,current signal and/or voltage signal) from an energy source (which iscoupled to the first circuit 115), the first circuit 115 induces acurrent in the second circuit 120 via a magnetic coupling between thefirst circuit 115 and the second circuit 120. In one example, the signalis a periodic pulse of energy. The signal (provided to and received bythe first circuit 115) is modulated for communication between the firstdie 105 and the second die 110. In an embodiment, the signal is providedto the first circuit 115 by an energy source on the first die 105.

For example, when the signal is a current, the current to the firstcircuit 115 is modulated using one of various modulation techniques,such as (but not limited to) on-off keying modulation, phase shiftkeying (PSK) modulation, amplitude modulation, phase modulation,quadrature phase shift keying (QPSK) modulation, and binary phase shiftkeying (BPSK) modulation. In on-off keying modulation, a combination of0s and 1s are used for modulating the current. In one example, an inputfor the on-off keying modulation is one of: 010101; 000010000100001; and11110111101111. In an embodiment, the signal provided to the firstcircuit 115 represents one or more bits. For example, in one embodiment,when the first circuit 115 receives a periodic pulse of energy, onepulse of energy represents one bit that is to be transmitted from thefirst die 105 to the second die 110.

In one embodiment, the first circuit 115 and the second circuit 120 areoscillators, such as LC tank oscillators, operating at a fixedfrequency. A magnetic coupling between the first circuit 115 and thesecond circuit 120 induces a current in the second circuit 120.Accordingly, the first circuit 115 and the second circuit 120 operate asmagnetically coupled oscillators at the fixed distance (d) 140. In anexample, such oscillators are injection locked oscillators. Themagnetically coupled first circuit 115 and the second circuit 120establish a near-field communication channel, which is suitable for usein high speed communication.

The first circuit 115 and the second circuit 120 operate at the fixedfrequency. In one example, the fixed frequency has a low gigahertz range(e.g., less than 3 GHz), so that the apparatus 100 is not required toperform high frequency (e.g., more than 60 GHz) signal processing. In anembodiment, the antenna coil is designed to maximize a coupling betweenthe first die 105 and the second die 110 when a quality factor (Q) is 10and the fixed frequency is less than 3 GHz.

In an example, the first circuit 115 and the second circuit 120 operateas LC tank oscillators. The LC tank oscillator in the first circuit andthe LC tank oscillator in the second circuit are configured to operateat the fixed frequency. A high speed communication is achieved betweenthe first die 105 and the second die 110, such as a communication whosespeed is faster than 500 Mb/s (megabits per second) and whose powerconsumption is relatively low at less than 10 mA current. In anembodiment, the first die 105 and the second die 110 include variouscircuit components for performing multiple tasks, which may continueuninterrupted during communication between the first circuit 115 and thesecond circuit 120. For example, in a microprocessor with the apparatus100, the microprocessor performs multiple tasks, which may continueuninterrupted even while the apparatus 100 operates as a wireless IO(input/output) for communication with other devices. In a first example,the wireless IO is performed concurrently with those multiple tasks. Ina second example, the wireless IO is performed during periods that arenon-overlapping with those multiple tasks. Further operation of theapparatus 100 is discussed in connection with FIG. 3.

FIG. 2 is a schematic diagram of an LC tank oscillator 200. The LC tankoscillator 200 includes an inductor (L) 205 and a capacitor (C) 215. Thevoltage across the LC tank oscillator 200 is V_(tank) 220. The LC tankoscillator 200 oscillates at a frequency f. The voltage decays due to aquality factor (Q) of the tank, which is represented as a resistor (Rp)210. When the voltage across the LC tank oscillator 200 is maximum, sothat V_(tank) is at peak, an energy contained in the LC tank oscillator200 is:E=1/2*C*V _(tank) ²  (1)Q is computed as:

$\begin{matrix}{Q = {2\pi\frac{{Maximum}\mspace{14mu}{Enery}\mspace{14mu}{Stored}\mspace{14mu}(E)}{{Power}\mspace{14mu}{loss}\mspace{14mu}(P) \times \left( \frac{1}{f} \right)}}} & (2)\end{matrix}$where f is a frequency of the LC tank oscillator 200. Accordingly, P isthe power loss or the power needed to sustain oscillation in the LC tankoscillator 200, which is:

$\begin{matrix}{P = \frac{2\pi\; f \times \frac{1}{2}{CV}_{tank}^{2}}{Q}} & (3)\end{matrix}$

As Q increases, less power P is needed. As V_(tank) 220 increases, morepower P is needed. Also, as frequency f increases, more power P isneeded to sustain oscillation in the LC tank oscillator 200.

FIG. 3 is a schematic diagram of coupled LC tanks 300 in operation ofthe apparatus 100. The coupled LC tanks 300 include a primary LC tankoscillator 302 and a secondary LC tank oscillator 312. The primary LCtank oscillator 302 includes a capacitor (C) 306, an inductor (L) 308,and a voltage source (Vin) 304. The voltage across the primary LC tankoscillator 302 is V_(p) 305. The voltage decays due to a quality factor(Q) of the primary LC tank oscillator 302, which is represented as aresistor (Rp) 310.

The secondary LC tank oscillator 312 includes a capacitor (C) 316 and aninductor (L) 314. The voltage across the secondary LC tank oscillator312 is secondary voltage (V_(s)) 315. The voltage decays due to aquality (Q) of the secondary LC tank oscillator 312, which isrepresented as a resistor (Rp) 318.

The primary LC tank oscillator 302 is similar to the first circuit 115on the first die 105, and the secondary LC tank oscillator 312 issimilar to the second circuit 120 on the second die 110. In one version,the first circuit 115 includes the primary LC tank oscillator 302, andthe second circuit 120 includes the secondary LC tank oscillator 312.The voltage source (Vin) 304 represents an energy source for the firstcircuit 115 and is configured to provide a signal to the first circuit115. The primary LC tank oscillator 302 and the secondary LC tankoscillator 312 operate at a same fixed frequency f as one another, sothey are in resonance. The fixed frequency f is also a natural frequencyof oscillation of the primary LC tank oscillator 302 and of thesecondary LC tank oscillator 312.

The voltage source (Vin) 304 provides a current to the primary LC tankoscillator 302. A magnetic coupling between the primary LC tankoscillator 302 and the secondary LC tank oscillator 312 induces acurrent in the secondary LC tank oscillator 312. In an embodiment, thevoltage source (Vin) 304 provides periodic pulses of energy to theprimary LC tank oscillator 302 at the fixed frequency f. In response tothe periodic pulses of energy, the primary LC tank oscillator 302oscillates at the fixed frequency f. This oscillation induces a forcedoscillation in the secondary LC tank oscillator 312 via a magneticcoupling between the first circuit 115 and the second circuit 120. Themagnetic coupling between the first circuit 115 and the second circuit120 in FIG. 1 is represented by a mutual inductance of the inductor (L)308 and the inductor (L) 314 in FIG. 3. In one example, if f=1 GHz, L=10nH, C=2.53 pF, and Q=10, then a relatively small amount of power P forsustaining oscillation in the primary LC tank oscillator 302 (andlikewise for sustaining oscillation in the secondary LC tank oscillator312) is 800 μW, according to equation (3). Such a relatively smallamount of power P is achievable even if a weak magnetic coupling existsbetween the primary LC tank oscillator 302 and the secondary LC tankoscillator 312. This small power P is provided as periodic pulses ofenergy to the first circuit 115 on the first die 105.

At a steady state, the secondary LC tank oscillator 312 operates as anLC tank oscillator with a driving voltage source 320 whose drivingvoltage is K*Vp, where K is a coupling coefficient between the primaryLC tank oscillator 302 and the secondary LC tank oscillator 312.Accordingly, the coupled LC tanks 300 can sustain oscillation for a lowcoupling coefficient (K) with a reasonable amount of power. A secondaryvoltage (Vs) 315 across the secondary LC tank oscillator 312 is:Vs=K*Vp*Q  (4)Vs=K*Vin*Q*Q  (5)Vs=K*Vin*Q ²  (6)

For example, if Q=10, then 100 times voltage amplification isachievable, which can offset a low coupling coefficient (K).Accordingly, when the primary LC tank oscillator 302 and the secondaryLC tank oscillator 312 operate at the same fixed frequency f as oneanother, the power transfer between them is highly efficient. In thatsituation, the primary LC tank oscillator 302 and the secondary LC tankoscillator 312 are in resonance, so the secondary voltage (Vs) 315 isstable and grows. By comparison, if the primary and secondary LC tankoscillators 302 and 312 were operating at different frequencies (e.g.,non-resonant frequencies), then the secondary voltage (Vs) 315 would notgrow.

FIGS. 4A-4C are graphs of modulation operations performed in theapparatus 100. With the resonant system approach of FIG. 3, the drivingcurrent and the secondary voltage (Vs) 315 are not directly controlled,and the secondary voltage (Vs) 315 builds over multiple cycles. Thecurrent in the primary LC tank oscillator 302 is modulated forcommunication between the primary LC tank oscillator 302 and thesecondary LC tank oscillator 312.

The current in the primary LC tank oscillator 302 is modulated using oneof various modulation techniques, such as (but not limited to) on-offkeying modulation, phase shift keying (PSK) modulation, amplitudemodulation, phase modulation, quadrature phase shift keying (QPSK)modulation, and binary phase shift keying (BPSK) modulation. Forexample, in one embodiment, the current in the primary LC tankoscillator 302 is modulated using on-off keying modulation, which takesadvantage of settling behavior of the coupled LC tanks 300. Thesecondary voltage (Vs) 315 is obtained on application of the on-offkeying modulation (M).

FIG. 4A shows operation when the on-off keying modulation (M) is 010101.FIG. 4B shows operation when the on-off keying modulation (M) is000010001000. Similarly, FIG. 4C shows operation when the on-off keyingmodulation (M) is 11110111101111. In an example, a transition from 1 to0 in this modulation is reduced by placing a low resistance in parallelin the primary LC tank oscillator 302.

FIG. 5 is a structural perspective view of apparatus 500, which is afirst alternative version of the apparatus 100 (FIG. 1). The apparatus500 includes at least a first die 502 and a second die 504. The firstdie 502 and the second die 504 are illustrative, and the apparatus 500may include multiple die and other active/passive components. The firstdie 502 includes at least a first circuit 506 and a second circuit 508.The second die 504 includes at least a third circuit 510 and a fourthcircuit 512. The first circuit 506 and the second circuit 508 arepositioned side-by-side on the first die 502, and the third circuit 510and the fourth circuit 512 are positioned side-by-side on the second die504, so that: (a) an edge of the first circuit 506 is parallel to anedge of the third circuit 510; and (b) an edge of the second circuit 508is parallel to an edge of the fourth circuit 512.

In a first embodiment, the first die 502 is integral with a firstconductive pad 520, and the second die 504 is integral with a secondconductive pad 525. The first conductive pad 520 and the secondconductive pad 525 both include multiple grooves to substantiallyprevent eddy current formation on the first conductive pad 520 and thesecond conductive pad 525 respectively. In a second embodiment, thefirst die 502 is integral with a first substrate (or chip) 520, and thesecond die 504 is integral with a second substrate (or chip) 525. In athird embodiment, the first conductive pad 520 and the second conductivepad 525 both include multiple cuts to substantially prevent eddy currentformation on the first conductive pad 520 and the second conductive pad525 respectively. In a fourth embodiment, when each of the first die 502and the second die 504 is integral with a non-conductive pad, thenon-conductive pad may optionally omit the multiple grooves.

In one example, the first die 502 and the second die 504 are integralwith a laminate, which substantially prevents eddy current formation. Inanother example, the first die 502 and the second die 504 are part ofdifferent packages, which are part of a PCB. In a different example, theapparatus 500 is integral with an MCM, so that the first die 502 and thesecond die 504 are on a single chip in the MCM. In a further example,the apparatus 500 is integral with an MCM, so that the first die 502 andthe second die 504 are part of different chips in the MCM. In yetanother example, the apparatus 500 is integral with a PCB.

In one version, the first die 502 is symmetrical with the second die504. The first die 502 is coplanar to the second die 504. The first die502 and the second die 504 are separated by a fixed distance (d) 515. Inan embodiment, the first circuit 506, the second circuit 508, the thirdcircuit 510 and the fourth circuit 512 include respective antenna coilswith non-radiative dimensions (e.g., non-radiative when an electricallength of the antenna coil is less than one-eighth of an operatingwavelength of the apparatus 500). In one example, the first circuit 506and the second circuit 508 are on-chip, and their antenna coils areintegral with a laminate. In one version, the second die 504 is on topof the first die 502, so that an active surface of the first die 502 isfacing an active surface of the second die 504, and each of those activesurfaces contains its respective antenna coil. In one embodiment, thefirst die 502 and the second die 504 are integral with a first packageand a second package respectively. In a further example, the secondpackage is on top of the first package, such that the active surface ofthe first die 502 is facing the active surface of the second die 504.

The first circuit 506 is coupled to a first energy source (not shown inFIG. 5), and the second circuit 508 is coupled to a second energy source(not shown in FIG. 5), such as a voltage source or a current source. Ina first example, the first die 502 includes the first energy source andthe second energy source. In a second example, the first energy sourceand the second energy source are external to the first die 502. In athird example, the first energy source and the second energy source areexternal to the apparatus 500.

The operation of the apparatus 500 is similar to the operation of theapparatus 100 (FIG. 1). The first circuit 506 and the third circuit 510operate at a first frequency. In response to a first signal (e.g.,current signal and/or voltage signal), the first circuit 506 induces acurrent in the third circuit 510 via a magnetic coupling between thefirst circuit 506 and the third circuit 510. In one example, the firstsignal is a periodic pulse of energy. The first signal (provided to andreceived by the first circuit 506) is modulated for communicationbetween the first circuit 506 and the third circuit 510. In anembodiment, the first signal is provided to the first circuit 506 by thefirst energy source on the first die 502.

The second circuit 508 and the fourth circuit 512 operate at a secondfrequency. In response to a second signal (e.g., current signal and/orvoltage signal), the second circuit 508 induces a current in the fourthcircuit 512 via a magnetic coupling between the second circuit 508 andthe fourth circuit 512. In one example, the second signal is a periodicpulse of energy. The second signal (provided to and received by thesecond circuit 508) is modulated for communication between the secondcircuit 508 and the fourth circuit 512. In an embodiment, the secondsignal is provided by the second energy source on the first die 502.

As discussed in connection with FIG. 3, when the primary LC tankoscillator 302 and the secondary LC tank oscillator 312 operate atdifferent (e.g., non-resonant) frequencies from one another, thesecondary voltage (Vs) 315 does not grow. In that manner, the apparatus500 achieves frequency selectivity, so that communication between thefirst circuit 506 and the third circuit 510 does not interfere withcommunication between the second circuit 508 and the fourth circuit 512.Accordingly, the apparatus 500 performs multi-channel communication inwhich: (a) a first channel operates at the first frequency forcommunication between the first circuit 506 and the third circuit 510;and (b) a second channel operates at the second frequency forcommunication between the second circuit 508 and the fourth circuit 512.

FIG. 6 is a structural perspective view of apparatus 650, which is asecond alternative version of the apparatus 100 (FIG. 1). The apparatus650 includes at least a first die 652 and a second die 654. The firstdie 652 and the second die 654 are illustrative, and the apparatus 650may include multiple die and other active/passive components. The firstdie 652 includes at least a first circuit 656 and a second circuit 658.The second die 654 includes at least a third circuit 660 and a fourthcircuit 662. The second circuit 658 is placed within the first circuit656 on the first die 652, and the fourth circuit 662 is placed withinthe third circuit 660 on the second die 654.

In a first embodiment, the first die 652 is integral with a firstconductive pad 670, and the second die 654 is integral with a secondconductive pad 675. The first conductive pad 670 and the secondconductive pad 675 both include multiple grooves to substantiallyprevent eddy current formation on the first conductive pad 670 and thesecond conductive pad 675 respectively. In a second embodiment, thefirst die 652 is integral with a first substrate (or chip) 670, and thesecond die 654 is integral with a second substrate (or chip) 675. In athird embodiment, the first conductive pad 670 and the second conductivepad 675 both include multiple cuts to substantially prevent eddy currentformation on the first conductive pad 670 and the second conductive pad675 respectively. In a fourth embodiment, when each of the first die 652and the second die 654 is integral with a non-conductive pad, thenon-conductive pad may optionally omit the multiple grooves.

In one example, the first die 652 and the second die 654 are integralwith a laminate, which substantially prevents eddy current formation. Inanother example, the first die 652 and the second die 654 are part ofdifferent packages, which are part of a PCB. In a different example, theapparatus 650 is integral with an MCM, so that the first die 652 and thesecond die 654 are on a single chip in the MCM. In a further example,the apparatus 650 is integral with an MCM, so that the first die 652 andthe second die 654 are part of different chips in the MCM. In yetanother example, the apparatus 650 is integral with a PCB.

In one embodiment, the first die 652 is symmetrical to the second die654. The first die 652 is coplanar to the second die 654. The first die652 and the second die 654 are separated by a fixed distance (d) 665. Inan embodiment, the first circuit 656, the second circuit 658, the thirdcircuit 660 and the fourth circuit 662 include respective antenna coilswith non-radiative dimensions (e.g., non-radiative when an electricallength of the antenna coil is less than one-eighth of an operatingwavelength of the apparatus 650). In one example, the first circuit 656and the second circuit 658 are on-chip, and their antenna coils areintegral with a laminate. In one version, the second die 654 is on topof the first die 652, so that an active surface of the first die 652 isfacing an active surface of the second die 654, and each of those activesurfaces contains its respective antenna coil. In one embodiment, thefirst die 652 and the second die 654 are integral with a first packageand a second package respectively. In a further example, the secondpackage is on top of the first package, such that the active surface ofthe first die 652 is facing the active surface of the second die 654.

The first circuit 656 is coupled to a first energy source (not shown inFIG. 6), and the second circuit 658 is coupled to a second energy source(not shown in FIG. 6), such as a voltage source or a current source. Ina first example, the first die 652 includes the first energy source andthe second energy source. In a second example, the first energy sourceand the second energy source are external to the first die 652. In athird example, the first energy source and the second energy source areexternal to the apparatus 650.

The operation of the apparatus 650 is similar to the operation of theapparatus 100 (FIG. 1). The first circuit 656 and the third circuit 660operate at a first frequency. In response to a first signal (e.g.,current signal and/or voltage signal), the first circuit 656 induces acurrent in the third circuit 660 via a magnetic coupling between thefirst circuit 656 and the third circuit 660. In one example, the firstsignal is a periodic pulse of energy. The first signal (provided to andreceived by the first circuit 656) is modulated for communicationbetween the first circuit 656 and the third circuit 660. In anembodiment, the first signal is provided to the first circuit 656 by thefirst energy source on the first die 652.

The second circuit 658 and the fourth circuit 662 operate at a secondfrequency. In response to a second signal (e.g., current signal and/orvoltage signal), the second circuit 658 induces a current in the fourthcircuit 662 via a magnetic coupling between the second circuit 658 andthe fourth circuit 662. In one example, the second signal is a periodicpulse of energy. The second signal (provided to and received by thesecond circuit 658) is modulated for communication between the secondcircuit 658 and the fourth circuit 662. In an embodiment, the secondsignal is provided by the second energy source on the first die 652.

As discussed in connection with FIG. 3, when the primary LC tankoscillator 302 and the secondary LC tank oscillator 312 operate atdifferent (e.g., non-resonant) frequencies from one another, thesecondary voltage (Vs) 315 does not grow. In that manner, the apparatus650 achieves frequency selectivity, so that communication between thefirst circuit 656 and the third circuit 660 does not interfere withcommunication between the second circuit 658 and the fourth circuit 662.Accordingly, the apparatus 650 performs multi-channel communication inwhich: (a) a first channel operates at the first frequency forcommunication between the first circuit 656 and the third circuit 660;and (b) a second channel operates at the second frequency forcommunication between the second circuit 658 and the fourth circuit 662.

FIG. 7 is a structural perspective view of apparatus 700, which is athird alternative version of the apparatus 100 (FIG. 1). The apparatus700 includes at least a first die 705 and a second die 710. The firstdie 705 and the second die 710 are illustrative, and the apparatus 700may include multiple die and other active/passive components. The firstdie 705 includes at least a first circuit 715, and the second die 710includes at least a second circuit 720.

In a first embodiment, the first die 705 is integral with a firstconductive pad 725, and the second die 710 is integral with a secondconductive pad 730. The first conductive pad 725 and the secondconductive pad 730 both include multiple grooves to substantiallyprevent eddy current formation on the first conductive pad 725 and thesecond conductive pad 730 respectively. In a second embodiment, thefirst die 705 is integral with a first substrate (or chip) 725, and thesecond die 710 is integral with a second substrate (or chip) 730. In athird embodiment, the first conductive pad 725 and the second conductivepad 730 both include multiple cuts to substantially prevent eddy currentformation on the first conductive pad 725 and the second conductive pad730 respectively. In a fourth embodiment, when each of the first die 705and the second die 710 are integral with a non-conductive pad, thenon-conductive pad may optionally omit the multiple grooves.

In one example, the first die 705 and the second die 710 are integralwith a laminate, which substantially prevents eddy current formation. Ina further example, the first die 705 and the second die 710 are part ofdifferent packages, which are part of a PCB. In another example, theapparatus 700 is integral with an MCM, so that the first die 705 and thesecond die 710 are on a single chip in the MCM. In a different example,the apparatus 700 is integral with an MCM, so that the first die 705 andthe second die 710 are part of different chips in the MCM. In yetanother example, the apparatus 700 is integral with a PCB.

The second die 710 is positioned at a fixed angle (α) relative to thefirst die 705. In one example, the fixed angle (α) is 180 degrees. Inanother example, the fixed angle (α) is an integer multiple of 45degrees. In one version, the first die 705 is symmetrical with thesecond die 710, so that dimensions (e.g., length, width and height) ofthe first die 705 are same as dimensions of the second die 710. Thefirst die 705 and the second die 710 are separated by a fixed distance(d) 740. In one example, the fixed distance (d) 740 is more than 0.5 mm.In a further example, the fixed distance (d) 740 varies from 0.5 mm to 7mm (millimeters). In another example, the fixed distance (d) 740 is suchthat a high voltage isolation (e.g., above 7.5 kilovolt) is maintainedbetween the first die 705 and the second die 710.

The first circuit 715 and the second circuit 720 include respectiveantenna coils with non-radiative dimensions (e.g., non-radiative when anelectrical length of the antenna coil is less than one-eighth of anoperating wavelength of the apparatus 700). In one example, the firstcircuit 715 is on-chip, and its antenna coil is integral with alaminate. In another example, the antenna coil is a flat coil (e.g.,flat spiral coil) having N number of loops in one plane, where N is aninteger. In one embodiment, the first die 705 and the second die 710 areintegral with a first package and a second package respectively. In afurther example, the second package is on top of the first package, suchthat the active surface of the first die 705 is facing the activesurface of the second die 710.

In an embodiment, the loops of the antenna coil and a capacitor togetheroperate as an LC tank (inductor capacitor tank) oscillator. In oneexample, each of the first circuit 715 and the second circuit 720includes a respective LC tank oscillator that is formed by a set ofinductors and a set of capacitors. Also, each of the first circuit 715and the second circuit 720 includes a respective transmitter and arespective receiver, which are used for communication between the firstdie 705 and the second die 710.

The first circuit 715 is coupled to an energy source (not shown in FIG.7), such as a voltage source or a current source. In a first example,the first die 705 includes the energy source. In a second example, theenergy source is external to the first die 705. In a third example, theenergy source is external to the apparatus 700. The operation of theapparatus 700 is similar to the operation of the apparatus 100 (FIG. 1).

Modifications are possible in the described embodiments, and otherembodiments are possible, within the scope of the claims.

What is claimed is:
 1. Apparatus comprising: a first die including aprimary LC tank oscillator having a natural frequency of oscillation toinduce a forced oscillation in a secondary LC tank oscillator of aseparate second die via a magnetic coupling between the primary LC tankoscillator and the secondary LC tank oscillator, the second dieseparated by a fixed distance from the first die.
 2. The apparatus ofclaim 1, wherein the first die includes the primary LC tank oscillatorhaving the natural frequency of oscillation to induce the forcedoscillation in the secondary LC tank oscillator of the second diecoplanar to the first die.
 3. The apparatus of claim 1, wherein thefirst die includes the primary LC tank oscillator having the naturalfrequency of oscillation to induce the forced oscillation in thesecondary LC tank oscillator of the second die at a fixed angle to thefirst die.
 4. The apparatus of claim 1, wherein the primary LC tankoscillator is configured to oscillate at the natural frequency inresponse to a signal from an energy source.
 5. The apparatus of claim 4,wherein the signal is modulated to communicate from the primary LC tankoscillator to the secondary LC tank oscillator via the magneticcoupling.
 6. The apparatus of claim 1, wherein the first die includes anantenna coil with non-radiative dimensions to communicate from theprimary LC tank oscillator to the secondary LC tank oscillator via themagnetic coupling.
 7. The apparatus of claim 1, wherein the first die isintegral with a conductive pad that includes grooves to prevent eddycurrent formation on the conductive pad.
 8. The apparatus of claim 1,wherein the natural frequency is a fixed frequency.
 9. The apparatus ofclaim 1, wherein the forced oscillation includes a current oscillation.10. Apparatus comprising: a first die including a primary LC tankoscillator having a natural fixed frequency of oscillation to induce aforced current oscillation in a secondary LC tank oscillator of aseparate second die via a magnetic coupling between the primary LC tankoscillator and the secondary LC tank oscillator, wherein the first dieincludes an antenna coil with non-radiative dimensions to communicatefrom the primary LC tank oscillator to the secondary LC tank oscillatorvia the magnetic coupling, the second die separated by a fixed distancefrom the first die.
 11. The apparatus of claim 10, wherein the first dieincludes the primary LC tank oscillator having the natural fixedfrequency of oscillation to induce the forced current oscillation in thesecondary LC tank oscillator of the second die coplanar to the firstdie.
 12. The apparatus of claim 10, wherein the first die includes theprimary LC tank oscillator having the natural fixed frequency ofoscillation to induce the forced current oscillation in the secondary LCtank oscillator of the second die at a fixed angle to the first die. 13.The apparatus of claim 10, wherein the primary LC tank oscillator isconfigured to oscillate at the natural fixed frequency in response to asignal from an energy source.
 14. The apparatus of claim 13, wherein thesignal is modulated to communicate from the primary LC tank oscillatorto the secondary LC tank oscillator via the magnetic coupling.
 15. Theapparatus of claim 10, wherein the first die is integral with aconductive pad that includes grooves to prevent eddy current formationon the conductive pad.
 16. Apparatus comprising: a first die including afirst LC tank oscillator having a natural frequency of oscillation toinduce a forced oscillation in a second LC tank oscillator of a separatesecond die via a first magnetic coupling between the first LC tankoscillator and the second LC tank oscillator, the first die including athird LC tank oscillator and the separate second die including a fourthLC tank oscillator, the first magnetic coupling between the first LCtank oscillator and the second LC tank oscillator to cause the first LCtank oscillator and the second LC tank oscillator to operate as a firstchannel independent from a second magnetic coupling between the third LCtank oscillator and the fourth LC tank oscillator, the first die mountedto a structure, the second die mounted to the structure.
 17. Theapparatus of claim 16, wherein the first LC tank oscillator isconfigured to oscillate at the natural frequency in response to a signalfrom an energy source.
 18. The apparatus of claim 16, wherein the firstdie includes an antenna coil with non-radiative dimensions tocommunicate from the first LC tank oscillator to the second LC tankoscillator via the first magnetic coupling.
 19. Apparatus comprising: afirst die including a primary LC tank oscillator having a naturalfrequency of oscillation to induce a forced oscillation in a secondaryLC tank oscillator of a separate second die via a magnetic couplingbetween the primary LC tank oscillator and the secondary LC tankoscillator, the first die integral with a conductive pad that includesgrooves to prevent eddy current formation on the conductive pad. 20.Apparatus comprising: a first die including a primary LC tank oscillatorhaving a natural fixed frequency of oscillation to induce a forcedcurrent oscillation in a secondary LC tank oscillator of a separatesecond die via a magnetic coupling between the primary LC tankoscillator and the secondary LC tank oscillator, wherein the first dieincludes an antenna coil with non-radiative dimensions to communicatefrom the primary LC tank oscillator to the secondary LC tank oscillatorvia the magnetic coupling, the first die is integral with a conductivepad that includes grooves to prevent eddy current formation on theconductive pad.